A progressive power lens is widely used in general because of an advantage that in appearance it is hardly detected from others as a spectacle for the aged in spite of a spectacle lens for presbyopia, an advantage that it allows a wearer to clearly look continuously from a far distance to a near distance without discontinuity, and so on. However, it is widely known that it presents disadvantages specific to the progressive power lens such that due to the necessity of arrangement of a plurality of visual fields such as a field for looking far, a field for looking near, and a field for looking at a distance intermediate therebetween, without a boundary line existing within a limited lens area, each visual field is not always sufficiently wide, and that there is a region mainly in a side visual field which causes the wearer to feel distortion or sway of an image.
Although many related arts have been proposed to improve these disadvantages, most of the related arts are related to designing techniques to give more preferred average dioptric power distribution or aberration distribution depending on the individual prescribed dioptric power and the wear state, and those focusing on the combination of right and left lenses and aiming for the improvement of a binocular vision function of right and left eyes are extremely scarce.
In these related arts, since design is carried out depending on the individual prescribed dioptric power and the wear state, the designs of right and left lenses become identical as long as the prescribed dioptric power and the wear state for right and those for left are the same. In this regard, since the directions of convergence of lines of sight in near vision become opposite between right and left, to express it more accurately, they are designed so as to be reflected in a mirror with the center between both eyes as a symmetric axis (generally referred to as mirror symmetry). The average dioptric power distribution and the aberration distribution are generally treated as “design” specific to each progressive power lens.
With the progress in designing techniques in recent years, designing methods to add “corrective action” have been enabled in order to eliminate or reduce the occurrence of astigmatism and variation in dioptric power mainly caused by a line of sight and a lens surface not being able to be orthogonal. This utilizes an optical designing technique referred to as ray tracing and is generally called “transmission design” and “aspherical design”, which is a designing method for obtaining an original optical function in a situation where a wearer actually wears the lenses. Any of an outer surface, an inner surface, and both surfaces of a lens can be subjected to the “corrective action” in principle, and due to the progress in the processing technology in recent years, the corrective action does not need to have been applied to a semifinished product prepared in advance but also it can also be applied by designing after receipt of an order.
However, the contents of the “corrective action” in conventional techniques are intended mainly to eliminate and reduce the occurrence of aberration and the variation in dioptric power associated with strong dioptric power and cylindrical dioptric power, and the design is only carried out depending on the prescribed dioptric power and the wear state of individual right and left eyes, so that it does not correspond to the difference between prescribed dioptric power of the right and left eyes.
As one of the conventional techniques to improve the inconvenience of a person who wears spectacles having different right and left dioptric powers, there has been a processing technology referred to as slab-off since early times. This mainly subjects only one region of a distance portion or a near portion of a lens to a cutoff processing for providing a vertical prismatic effect in order to eliminate a vertical prism difference in right and left near visions. Regarding this slab-off, as a more detailed resource disclosed to public, there are “'82 HOYA Senior Lens Fabrication Dioptric Power Range Table (since February 1, 1987) p. 45” and the like.
In the above-described conventional technique, there are disadvantages, that a boundary line (ridge line of bending surfaces) of two types of intersecting surfaces is generated at the border between the distant and close regions of a lens subjected to a cutoff processing, thereby being distinct and that a jump of an image, referred to as an image jump, is generated as a result of an abrupt change in the prismatic effect at the boundary line as a border. It should be noted that, although the slab-off can be applied to progressive power lenses, the occurrence of a horizontal boundary line between the distant and close regions is inevitable and an important merit of “not having a boundary line” in normal progressive power lenses turns out to be lost.
In addition, there has been proposed a method for eliminating or reducing a vertical prism difference in right and the left near visions without the occurrence of such a boundary line for progressive power lenses having different right and left distance dioptric powers (refer to Patent Document 1).
This technique is intended to provide a difference between the prismatic power in the near portion for right and left eyes by providing a difference in the way the dioptric power changes in right and left progressive corridors. For example, even when the addition power is the same, average addition power in progressive corridors becomes different in a case where the variation of dioptric power in the progressive corridors extending from the distance portion to the near portion increases moderately at first and rapidly at last and, on the contrary, in a case where it increases abruptly at first and gently at last, and thus a difference is generated in a vertical prismatic effect in the near portion separated below by a certain distance from the distance portion. By compensating for the prism difference, the vertical prism difference in the near portion caused by the difference between the right and left distance dioptric powers described above can be decreased. However, since the right and left addition powers in the middle of the progressive corridors are different in this method, there is a problem of the occurrence of the inconvenience for a binocular vision in intermediate vision.
The common concept in these conventional techniques is to eliminate the difference between right and left prisms itself caused by the difference between right and left distance dioptric powers. However, in the former method of slab-off to generate a boundary line, “continuity of visual field” is lost, which is extremely important for progressive power lenses. In addition, in the latter method of changing the dioptric power in the progressive corridors described in Patent Document 1, although the “continuity of visual field” is maintained, the intermediate visual field viewed through the progressive corridors is damaged.
Meanwhile, there are conventional techniques intended not to eliminate the prism difference itself but to reduce the adverse effect due to the shift of lines of sight resulted from the prism difference by changing the aberration and dioptric power distribution of the lenses.
FIG. 21 is a diagram illustrating a horizontal prism difference occurring when viewing a near visual target TN in a distance of, for example, 40 cm on the front with a left eye 12L and a right eye 12R by progressive power lenses 11L and 11R having different near dioptric power for right and left and a change in the orientation of the lines of sight by the right and left eyes resulted therefrom. Here, indexes R and L of each reference numeral or character in the drawing correspond respectively to the right and left eyes, and points OL and OR denote centers of rotation of eye, points PL0 and PR0 denote intersections of lines of sight in frontal vision with outer lens surfaces, points PL and PR denote intersections of lines of sight in near vision with outer lens surfaces, HL and HR denote amounts of displacement corresponding to convergence actions of eyes from frontal vision to near vision, broken arrows EL and ER denote directions of eye axes, and solid arrows VL and VR denote directions of lines of sight from the lenses to the visual target TN. In the example illustrated in FIG. 21, it is understood that the differences between the eye axis direction and the line-of-sight direction are different between right and left due to the difference of the prismatic effects of the right and left lenses 11L and 11R at the intersections of the lines of sight in near vision with the outer lens surfaces.
When viewing the near visual target TN on the front with the use of such progressive power lenses having different right and left near dioptric powers, in order to obtain a good binocular vision, it is desirable that the addition power at the intersections between the lines of sight and the lenses, which are passing positions of the lines of sight on the lenses, are equal to each other and the astigmatism is zero. Accordingly, it is effective to change amounts of displacement, generally referred to as “amounts of inset in near portions”, in response to the near dioptric power (more in detail, horizontal components of the near dioptric power) in order to obtain a good binocular vision. Such related arts are called by the name of “ergonomic inset”, “variable inset”, or the like, and are already commercialized.
In addition, for example, progressive power lenses of a product name Evolis have been available on the market, manufactured by BBGR, in France in the year 2001 at the latest, and they are varied so as to have a small amount of the inset and a short length of the progressive corridor for presbyopia with myopia, a large amount of the inset and a long progressive corridor for presbyopia with hyperopia, and an intermediate amount and length between them for presbyopia with emmetropia.
These designing approaches are designed with an intention of “not reducing the difference itself between right and left prisms but reducing a secondary adverse effect therefrom”.
However, these related arts only classify the changes in the passing positions of the line of sight in near vision extremely simply and cope with them, which cannot be sufficient improvement.
For example, the related arts, such as “ergonomic inset” and “variable inset”, cope only with horizontal positional shifting and do not cope with vertical positional shifting.
In addition, the Evolis classifies the distance dioptric power only into three types of myopia, hyperopia, and emmetropia. Accordingly, no matter how greatly the right and left distance dioptric powers differ, they are subjected to no improvement in a case where the right and left eyes are classified as being the same. Even if right and left classifications are different, since there are only three types of classifications, an improvement deals with only three types of combinations of “myopia and emmetropia, emmetropia and hyperopia, and myopia and hyperopia”, which cannot be said as an improvement in response to the dioptric power difference between the right and left distance dioptric powers.
Even if the distance dioptric power is classified even more finely and various combinations of an amount of inset and a length of the progressive corridor are set in accordance with the classification, the configuration of determining the design for single eye by the use of the distance dioptric power for the single eye does not change. That is, as long as the relationship with another distance dioptric power on the other side is not considered, the progressive power lenses cannot be regarded as corresponding to the binocular vision.
Moreover, these related arts propose only the position alignment of near visual fields of the right and left eyes, and there is no conventional technique that proposes an improvement of a binocular visual field in all visual field regions of progressive power lenses, such as distant vision, side vision, near vision, and intermediate vision.
In addition, there has been proposed techniques that allow viewing an object in the same posture as in the “previous lens” in response to the dioptric power change and the refractive index change of the material due to the replacement of progressive power lenses (for example, refer to Patent Document 2). However, in this case, the invention is merely intended to reduce a feeling of difference from the “previous lens” by the replacement of the spectacles and is not intended to improve the binocular visual field.
Further, although there are generally known techniques to, for example, align curves and thicknesses on the front side of the right and left lenses with each other in a case where the difference of dioptric power is present, they are neither the techniques to disclose an improvement of binocular visual fields of all visual field regions in progressive power lenses such as distant vision, side vision, near vision, and intermediate vision, in the configuration of the progressive power lenses described above, nor the techniques to propose configurations of an average dioptric power distribution and an astigmatism distribution for a binocular vision.
[Patent Document 1] Japanese Patent Publication No. 3788083
[Patent Document 2] Japanese Unexamined Patent Application Publication No. 2006-285200